Hey everyone, I am building a large 3d printer around 300mmx300mmx500mm. But Im trying to figure out the best budget heatbed solution. I have a silicon heater but am stuck between aluminum plate, cast aluminum plate, and borosilicate glass. I wouldnt mind getting aluminum then eventually getting glass but aluminum tends to warp. Cast alum will cost a pretty penny, but will a thick rolled aluminum plate work? Will a 1/4" or 1/2" cause any warping? Should I go for 6061, 5052, or 3003? Thanks 
The difference in linear thermal expansion between different aluminum alloys is so small it’s hard to measure, so use whatever’s cheapest.
Thicker aluminum adds weight where you don’t want it. I’m not sure that’s the right direction to go. What it does get you is better heat distribution, and it’s having varying temperatures across the plate that makes it warp.
Do you have any local aluminium scrapyards? I’ve bought mic6 cast-then-ground for basically scrap prices, $2/kg, at my local scrapyard, when they have it.
You should get the MIC 6 alum. That is already pregrounded
Ill have to check, but there arent many friendly ones. To clarify thick aluminum means better heat distribution? I dont believe weight will be a issue. Using two 64oz nema 17’s for the bed.
My current remaning budget for the aluminum plate is 25. Now I can get a 12x12"x1/2" 6061 aluminum plate for $15 or a 10.75x12.5x.25" cast aluminum plate for 20. From what ive seen, a 12x12 mic6, cast aluminum, or tooling jig is at least 40. I need at least 300mmx300mm (12x12) to full adhear silicon bed. Probably sound really cheap. But one thing I have is time. As Benjamin Franklin said, “Time is money”.
The timee you will spend to flat the 6061 will cost you more than the mic 6!..
Got it. I will have to wait or find a good place to buy it. I am open to any suggestions.
I have the exact same dimension printer: I have the makerfarm 12x12" heated bed with a removable aluminum 1/4" tooling plate on top (which I notched via my cnc to fit over the heated bed bolts, and to run a slot for the thermistor in the middle), with PEI stock on top of that. Has been working great, for PLA at least, which is what I mainly print with. I used double-thick glass before that, but surprisingly, it actually did sag in the middle slightly. Have had no issues with the tooling plate. I paid $20 for mine online, plus another $20 for shipping 
My local metal supplier wanted $45 for it, plus tax :S
This is where I got mine, if you want to go that route:
https://www.midweststeelsupply.com/store/castaluminumplateatp5